Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Carbon dioxide

Freon

Ammonia

2. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

30 bar

15 bar

2 bar

3. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

Good electrical conductor

High risibility with oil

4. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

5. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

6. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Rankine

Reversed Carnot

7. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

Takes place at constant entropy

8. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

Absorber

9. Critical temperature is the temperature above which

Water will never evaporate

A gas will never liquefy

Water will evaporate

A gas will immediately liquefy

10. The capillary tube, as an expansion device, is used in

All of these

Room air conditioners

Water coolers

Domestic refrigerators

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11. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Any one of the above

Equal to unity

Always less than unity

12. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 1

1: 9

1: 3

13. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.6

0.4

14. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

None of the above

Ensures the evaporator completely filled with refrigerant of the load

15. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

16. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

17. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

18. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

One heat exchanger

Four heat exchangers

19. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

20. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Collect vapours

Detect liquid in vapour

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21. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

4.33

1.33

3.33

22. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Positive

None of these

Zero

23. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

24. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

25. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

26. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

27. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Sub-cooling or under-cooling

Normal cooling

Super-cooling

28. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

29. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

30. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Piston type reciprocating

Axial

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31. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

5°C

20°C

32. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

33. Rating of a domestic refrigerator is of the order of

0.1 ton

40 tons

10 tons

5 tons

34. For obtaining high COP, the pressure range of compressor should be

Low

Optimum

Any value

High

35. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

36. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-77.7°C

-135.8°C

37. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Stirling

Carnot

Ericson

38. In a lithium bromide absorption refrigeration system

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

39. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

40. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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